Re: Transformer drawing 1 amp

Thanks guys,

Could someone explain why and how a transformer limits its current?
They all look the same to me. I know there is saturation of the core
that limits stuff but I don't know any details about it. It seems that
the only parameters that one can change(the main ones at least) are
the winding ratio and total windings. (assuming standard transformer
design) I suppose if you just have one winding on the secondary and
100 on the primary its not going to function as well as if you have
100 windings on the secondary and 10000 on the primary.

In any case, I'm testing the transformer as we speak. Its been running
for about 40 mins and now has a temperature of about 37C. For the
first 20 mins its was quite cool and maybe rose about 5 degree's above
ambient. My meter is telling me that its drawing 0.8A but another
meter said it was only about 0.6A when I tested it. Not sure if the
meters are bad, if it has something to do with the inductance, or I
just made a mistake... or maybe the meters are not calibrated
properly.

I had another transformer that is 25VCT @ 2A and it was drawing about
0.1A without any load. I suppose if everything scales up linearly then
the 0.8A is reasonable. Its already at 40C and drawing about 0.90A
(it slowly has seemed to creep up from about 0.84A at the start to
0.9A now) so is I draw another 1.5A from it then I'm sure it will get
to hot.

It seems to bee peaking out at about 42C(the current has dropped to
about 0.84A) but I could be wrong. Its hot to the touch but not close
to burning but if one presses pretty hard then it does get
uncomfortable and feels like it might burn after a short time. I can
only imagine that having a full load on it will make it impossible to
use and will most likely burn it up? Also I'm not sure how well my
thermometer is measuring the actual temperature. I do not smell any
smoke or fumes of any kind either.


What should I do? Chances are I will run the power supply for long
durations and rarely will I draw more than a few amps and when I do it
will be for short periods of time(in most circumstances). I just need
something with a little more juice than my current ps for those rare
occasions when I want to play with things like electromagnets and
motors. Although I don't want to take any chance have the thing burn
down the house either.

If some transformers are designed in this way(to run "hot") could
someone please explain why? I'm at a loss as to explaining the
behavior of this transformer if its not broke but besides the extra
current everything else seems, at least so far, to be ok. Although
when that extra 15 amps goes through the secondary and extra 1.5A
going through the primary probably spells disaster?

Thanks,
Bob

.

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